The present invention relates generally to a paintbrush embedment compound and also to a paintbrush construction and method of manufacture utilizing such embedment compound. More particularly, the present invention relates to a paintbrush construction of the type which preferably includes a ferrule, a plurality of bristles and a handle and a method of manufacturing the same utilizing an improved embedment compound comprising a highly crosslinked polyurethane composition for bonding the plurality of bristles to one another.
The method of manufacturing brushes such as paintbrushes and the like has remained relatively unchanged for a number of years. A conventional paintbrush consists of three basic elements: the bristles, which may be either natural or synthetic, the ferrule which is commonly a lightweight metal functioning to hold the potted or bundled bristles, and a handle secured to the upper portion of the ferrule. During a conventional brush manufacturing procedure, the bristles are bundled and then potted or inserted into the ferrule. Following this potting step, a bristle adhesive or embedment compound is introduced into the ferrule portion and allowed to flow downwardly into the bristles and at the same time cure and harden so as to bond the bristles to one another. The adhesives initially used for this purpose were rubber based adhesives. Sometime after World War II there was a revolution in which the previously used rubber based adhesives were replaced with epoxy adhesives. The use of epoxy adhesives for bonding the bristles together continues to be used today, almost without exception.
While epoxy adhesives and resins have been satisfactory in many applications, they also have some recognized deficiencies. For example, the ability of epoxy adhesives to bond the bristles together and to bond the bristles to the inside surface of the ferrule is limited. Further, epoxy adhesives function differently depending upon the particular material from which the bristles are constructed. Some epoxy adhesives work well with natural bristles, but not with synthetic bristles; whereas, others work well with some synthetic bristles, but not others. Thus, it is necessary and customary for brush manufacturers to maintain inventories of several different epoxy adhesives to accommodate the various bristle materials. Even when the proper epoxy adhesive is selected from the bristle material, it is generally recognized that there is very little bonding between the bristles and the inside surface of the ferrule. Because of this, there is an increased number of bristles pulled out and lost during the painting process and in some cases the entire bristle bundle can be pulled from the ferrule. The primary limitation, however, of epoxy adhesives is the amount of time normally required for curing. The normal cure time for commonly used epoxy adhesives ranges from four to twenty-four hours. Accordingly brushes constructed utilizing an epoxy adhesive do not readily facilitate a continuous manufacturing process. Although the cure time for the epoxy adhesives can be speeded up through the use of heat or accelerators, the viscosity is usually adversely affected and the fast setting epoxies are very exothermic. This causes shrinking of the cured adhesive as it cools. A further disadvantage of the relatively slow curing epoxy adhesives is that it significantly slows down the quality control evaluation. Thus, if the formulation is not correct or the penetration is unsatisfactory, a large quantity of brushes (usually several hundreds or thousands) will have been made before the error is discovered.
Accordingly, although the use of epoxy adhesives and resins in the manufacture of brushes such as paintbrushes and the like are acceptable in some applications, there are several limitations and disadvantages which exist because of the use of these adhesives.